In many treatments apparatus are used to provide patients with air. More frequently it is used for patients with a breathing deficiency caused for example by the weakness of the breathing system or by obstructive apneas during the sleep. In those cases it is important to control the pressure of the air delivered to the patient. With respiratory insufficient patients, apparatus providing air at a higher pressure help to compensate the weakness of the patients lungs. In the case of patients suffering of sleep apneas, providing the air at a higher pressure removes the obstruction of the upper airways.
In order to provide a correct treatment, it is required to accurately know the value of airflow the patient is provided with. Usually the apparatus determine the airflow by measuring airflow in the patient circuit (between the blower and the mask) using an airflow sensor. Airflow sensors can be based on high sensitivity differential pressure sensors measuring the pressure drop across a low resistance or using pitot tubes, or hot wire airflow sensors. Another commonly used mean to evaluate the airflow is by measuring the blower parameters such as speed, current consumption and power.